(1) Field of the Invention
The present invention relates to crystalline silicon plates, a process for growing crystalline silicon plates, a crystalline silicon plate-growth apparatus, and solar cell elements using crystalline silicon plates as substrates.
(2) Related Art Statement
The crystalline silicon solar cell is produced by the four steps of preparing a raw silicon material, producing a substrate from the raw silicon material, forming a cell structure on the substrate, and converting the cell structure into a module. The silicon substrate is ordinarily produced by the Czochralski process (CZ process: pulling-up process) (See "Cell Manual" published by Maruzen Co., Ltd.). Further, a lateral type crystal continuous growth apparatus has been known for growing silicon crystal plates for solar cells.
However, in such a lateral type crystal continuous growth apparatus, it was impossible to uniformly and continuously grow a crystalline silicon plate having an extremely small thickness. For example, a thickness of less than 200 .mu.m. On the other hand, according to the Czochralski process, a cylindrical silicon crystal may be grown, but then must be cut. Furthermore, it is known that a crystalline silicon plates can be made by growing a polycrystal body according to the casting process and cutting it. However, according to such growing methods, a large percentage the silicon crystal which cut is thrown away. As a result, a lot of the material is wasted, resulting in a high crystal-growing production cost. Therefore, it is difficult to reduce production costs the solar cell element. Since silicon is scarce as a natural source and its material cost is high, this leaded to increase in the production cost of silicon based solar cell elements.
In order to produce the solar cell element, a P-type or N-type diffusion area is formed at a surface of a crystalline silicone plate by diffusing a dopant element thereinto to obtain a P-N junction. However, such a diffusing process is complicated, which is a large factor to raise the production cost.